Her voice was calm, yet steely. It was Alice Hoagland, and she was calling her son, a passenger on the doomed Flight 93.

"The news is that it's been hijacked by terrorists," she said. "I would say go ahead and do everything you can to overpower them, because they're hell-bent."

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Those words are part of a voicemail message made public for the first time by the National September 11 Memorial & Museum, which on Wednesday released a new multimedia timeline of the attack.

Hoagland's son, Mark Bingham, and his fellow travelers died when the Newark-to-San Francisco flight crashed in Shanksville, Pa. Authorities believe the 9/11 hijackers intended to steer it toward the White House or the Capitol.

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After she urged him to gather other passengers and make a move, Hoagland concluded the call. "I love you sweetie. Good luck. Bye-bye."

The message, lasting less than a minute, is part of a new trove of audio and visual reminders of 9/11 now available to the public as the 10th anniversary of the attacks approaches.

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The timeline starts at 5:45 a.m., with photographs of hijackers Mohammed Atta and Abdulaziz al-Omari passing through airport security in Maine for a flight to Boston, where they would board Flight 11. It ends at 8:30 p.m., with President George W. Bush addressing the nation.

Along the way, it outlines the departures of all four fatal flights and shows images of their passenger manifests, video and photos of the World Trade Center's north and south towers after they were hit and heart-breaking moments such as when United Airlines Flight 175 passenger Brian Sweeney left a voicemail for his wife, Julie Sweeney.

"Jules, it's Brian. Listen, I'm on an airplane that's been hijacked. If things don't go well, it's not looking good, I just want you to know I absolutely love you," he said.

The timeline doesn't shy away from the starkest images of the day. In one video of the collapse of the south tower, an onlooker can be heard saying, "Oh, my God!" repeatedly as the tower falls. A video of the fall of the north tower carries a warning of mature language, as people can be heard screaming and cursing, including a man saying, "That's a (expletive) bomb!"

The president of the museum, Joe Daniels, said the project's organizers were sensitive to the nature of what they were presenting and took steps such as leaving it up to viewers as to whether they wanted to take closer looks at specific photographs and videos or listen to particular bits of audio.

"We are the institution that needs to preserve the history of what happened," he said. "That means taking on some of the difficult material. That means reminding people of some of the difficult stuff."

Charles G. Wolf, who lost his wife, Katherine Wolf, at the World Trade Center, said it was a good thing that the museum was putting this material out there.

"We don't want it to be sugarcoated," he said. "We want people to understand what it was like."

The images may be difficult for some Sept. 11 family members and others to look at, but they can choose not to, Wolf said. He contrasted that to what he expects the atmosphere will be like closer to the 10th anniversary in September, when it's likely images from the event will be more prevalent on television and elsewhere and will be more difficult for people disturbed by them to avoid.

"Unless you choose not to turn the television on, you're going to be hit by this stuff later this year," he said.

The destruction at the Pentagon, the evacuation of lower Manhattan and the few extrications of people trapped in the debris are all in the timeline, as are images of items including the dusty and dirty shoes that were worn by people as they left the stricken towers and political candidates' notices for the primary election New York City was expecting to hold that day.

Compiled from the museum's collection, the timeline is an effort to help people get a sense of how that life-altering day unfolded, Daniels said.

"It takes an incredibly chaotic day that changed the world and organizes it in a way that is accessible to large numbers of people," he said, pointing out, "No matter where you were, it was confusing."

The timeline's use of social media allows viewers to share it in a personal way, said Mike Lucaccini and Danny Riddell, founders of Archetype International, the San Francisco-area company that designed and developed it. If there's a particular moment of the day that someone wants to share, he or she can do that.

"It's such a personal experience for everyone," Lucaccini said. "A specific moment in time may mean something to someone in particular."

Other newly released artifacts include dust-covered uniforms of police and firefighters and interviews with survivors -- the office workers who made it out of the World Trade Center.